<h4>Tool</h4><table border="0"><tr><td valign="top"><b>Name</b></td><td valign="top">Flow Path Length</td></tr><tr><td valign="top"><b>ID</b></td><td valign="top">6</td></tr><tr><td valign="top"><b>Author</b></td><td valign="top">O.Conrad (c) 2005</td></tr><tr><td valign="top"><b>Specification</b></td><td valign="top">grid</td></tr></table><hr><h4>Description</h4>This tool calculates the average flow path length starting from the seeds, that are given by the optional 'Seeds' grid and optionally from cells without upslope contributing areas (i.e. summits, ridges). Seeds will be all grid cells, that are not 'no data' values. If seeds are not given, only summits and ridges as given by the flow routing will be taken into account. Available flow routing methods are based on the 'Deterministic 8 (D8)' (Callaghan and Mark 1984) and the 'Multiple Flow Direction (FD8)' (Freeman 1991, Quinn et al. 1991) algorithms.

References:

Deterministic 8
- O'Callaghan, J.F. / Mark, D.M. (1984):
    'The extraction of drainage networks from digital elevation data',
    Computer Vision, Graphics and Image Processing, 28:323-344

- Freeman, G.T. (1991):
    'Calculating catchment area with divergent flow based on a regular grid',
    Computers and Geosciences, 17:413-22

- Quinn, P.F. / Beven, K.J. / Chevallier, P. / Planchon, O. (1991):
    'The prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models',
    Hydrological Processes, 5:59-79

<hr><h4>Parameters</h4><table border="1" width="100%" valign="top" cellpadding="5" rules="all"><tr><th>Name</th><th>Type</th><th>Identifier</th><th>Description</th><th>Constraints</th></tr>
<tr><th colspan="5">Input</th></tr><tr><td>Elevation </td><td>Grid (input)</td><td>ELEVATION</td><td></td><td></td></tr><tr><td>Seeds (*)</td><td>Grid (optional input)</td><td>SEED</td><td></td><td></td></tr><tr><th colspan="5">Output</th></tr><tr><td>Flow Path Length</td><td>Grid (output)</td><td>LENGTH</td><td></td><td></td></tr><tr><th colspan="5">Options</th></tr><tr><td>Seeds Only</td><td>Boolean</td><td>SEEDS_ONLY</td><td>Use only seed cells as starting points.</td><td>Default: 0</td></tr><tr><td>Flow Routing Algorithm</td><td>Choice</td><td>METHOD</td><td></td><td>Available Choices:
[0] Deterministic 8 (D8)
[1] Multiple Flow Direction (FD8)
Default: 1</td></tr><tr><td>Convergence (FD8)</td><td>Floating point</td><td>CONVERGENCE</td><td>Convergence factor for the 'Multiple Flow Direction' algorithm (after Freeman 1991)</td><td>Minimum: 0.000000
Default: 1.100000</td></tr></table>(*) <i>optional</i>